(not applicable)
The invention relates generally to a combination satellite and terrestrial antenna, and more particularly to a combination linearly polarized and quadrifilar antenna able to provide excellent performance for both antennas.
Charles D. McCarrick describes a combination monopole/quadrifilar helix antenna for S-band/Satellite applications on page 330 of the May 2001 edition of the Microwave Journal. FIG. 1 illustrates the monopole/quadrifilar antenna 10 discussed in the McCarrick article. The antenna 10 includes a monopole 15 whose reflective element is a quarter-wave choke 14. Elements 14 and 15 form dipole antenna 13. The antenna 10 comprises a coaxial line 12 with a section of the outer conductor removed to expose the center conductor 15. The quarter-wave choke 14 is placed within a quadrifilar helix antenna shell 16 in an axially concentric fashion. The quadrifilar helix antenna is typically phased to produce circular polarization. Appropriate placement of the dipole antenna 14 within the quadrifilar antenna is critical for avoiding coupling between the two antennas and avoiding degradation of radiation patterns.
A combined antenna as described above has the disadvantages of having strict design requirements in terms of relative placement between antennas to avoid interference between the antennas and further requires a wider overall structure that may not necessarily be aesthetically pleasing. It is very difficult to optimize due to interactions between the dipole and quadrifilar helix. Furthermore, it is a mechanically-challenging structure and difficult to manufacture. The typical placement for such a combined antenna would be on the sloping back windshield of a vehicle. In this instance, for good satellite reception, care must be taken to ensure that most of the quadrifilar antenna xe2x80x9cclearsxe2x80x9d the line of sight with the transmitting satellite that may be blocked by the roof of the vehicle. Thus, a need exists for a combined dipole and quadrifilar antenna that will enable designers further freedom in the relative placement of the antennas while avoiding the detriments of coupling and interference between the antennas. Further, a need exists for a combined antenna that is esthetically pleasing that will further enable greater design choice in the placement of such combined antennas on windshields without being subject to blockage of signals by the form factor of the vehicle.
In a first aspect of the present invention, a combination linearly polarized antenna and quadrifilar helix antenna comprises a quadrifilar antenna having a first coaxial cable and an antenna with linear polarization external to the quadrifilar antenna and having a second coaxial cable. A center conductor of the second coaxial cable is isolated from a center conductor of the first coaxial cable and the first coaxial cable runs substantially concentrically through the antenna with linear polarization.
In a second aspect of the present invention, a combination dipole and quadrifilar helix antenna comprises a quadrifilar antenna having a first coaxial cable and a dipole antenna external to the quadrifilar antenna and having a second coaxial cable. A center conductor of the second coaxial cable is isolated from a center conductor of the first coaxial cable and the second coaxial cable runs substantially concentrically through the quadrifilar helix antenna.
In a third aspect of the present invention, a combination linearly polarized antenna and quadrifilar helix antenna comprises a quadrifilar antenna and a linearly polarized antenna vertically aligned and external to each other. The combination antenna further comprises a first coaxial cable running substantially concentric within at least a portion of the combination linearly polarized antenna and quadrifilar helix antenna serving as a coaxial feed to a quadrifilar feed network for the quadrifilar antenna and a second coaxial cable running substantially concentric within at least a portion of the combination linearly polarized antenna and quadrifilar helix antenna and serving as a quarter-wave extension for the linearly polarized antenna.
In a fourth aspect of the present invention, a tubular dipole antenna comprises a coaxial cable having and an inner conductor and an outer conductor both running vertically and substantially concentrically through a quarter-wave metal sleeve. The tubular dipole antenna further comprises a shorted end formed from the connection of the outer conductor of the coaxial cable to an end of the quarter-wave metal sleeve and a quarter-wave hollow metal tube connected to the inner conductor of the coaxial cable extending from the end of the quarter-wave metal sleeve.